study of theories about myopia progression (stamp)

Conditions: Myopia

Summary: at this time, we do not know what causes a child to become more nearsighted (myopic). stamp will help us better understand nearsightedness in children. children will be randomly chosen to wear regular glasses (single vision lenses) or no-line bifocal glasses (progressive addition lenses) for the first year of the study. all children will wear regular glasses for the second year of the study. stamp will compare how the eye changes shape in the two groups to help us understand why children become nearsighted. the two theories of myopia progression that are being evaluated are based on different factors. one theory is based on environmental factors such as extended near work while the other theory is based on genetically coded factors.

eligible children will be enrolled, randomized, and followed at six-month intervals for two years with all children wearing single vision lenses for the second year. at each visit, complete measurements of the components of the eye will be made to explain the mechanism responsible for the progressive addition lens (pal) treatment effect and why it occurs mainly during the first year of bifocal wear (gwiazda et al. 2003). while hyperopic retinal blur (blur at the back of the eye) due to accommodative lag (poor focusing when doing close work) has been proposed as a possible mechanism driving myopia progression (gwiazda et al. 1993), others have shown that accommodative lag accompanies rather than precedes the onset of myopia (mutti et al., 2006). this suggests that accommodative lag is a result of another possible mechanism resulting in myopia progression such as crystalline lens-induced ciliary-choroidal tension (a model in which the lens in the eye is stretched and is not as good at focusing up close) (mutti et al., 2000). according to this proposed mechanism, high accommodative lag in myopia results from increased crystalline lens tension that is transmitted through the choroid (an outside layer of the eye). this tension results in restricted equatorial (the vertical dimension of the eye) eye growth with no axial (front to back) restriction to eye growth and yields a prolate ocular shape (an eye that is longer than it is wide) in myopes (mutti et al., 2000). comparisons: refractive error (glasses prescription), axial length (length of the eye), peripheral eye shape, accommodation (focusing ability), corneal shape (shape of the front of the eye), anterior chamber depth, crystalline lens thickness and curvatures (shape of the lens in the eye), central and peripheral higher-order aberrations (how well light focuses in the eye), and phoria (eye alignment) will be measured at six-month intervals. the primary study outcome is refractive error measured by cycloplegic autorefraction. comparison of the biometric data collected both during the first year when the pal intervention is present and during the second year when the pal intervention is removed will allow us to differentiate between the two theories under consideration. we will also evaluate whether the modest pal treatment effect that has been reported during the first year of pal wear is permanent.

Eligibility criteria:
inclusion criteria: * 6 to 11 years of age * best corrected vision of at least 20/30 in each eye * birth weight \> 1250g (the criteria below will be evaluated at a screening visit to find out if the child can participate) * accommodative lag \>= 1.30 d (for a 4d stimulus) * at least -0.75 d myopia in each meridian measured with cycloplegic autorefraction but not more than -4.50 d in each meridian in each eye * esophoria at near if more than -2.25 d spherical equivalent (high myopia) * astigmatism \< 2.00 dc in each eye * anisometropia \< 2.00 d exclusion criteria: * strabismus (eye turn) * history of contact lens wear * history of previous bifocal wear * diabetes mellitus

Keywords: myopia progression bifocal